I have ben doing a little searching and have found some useful information but still a little confused....I have a 383 fully forged bottom end with 8.5:1 CR, AFR 195 Heads, BB custom Cam, and a procharger. I am having some trouble with low vaccum....if i read correctly, if i subtract the Map reading from the Baro reading then that should give me my vacuum reading correct? if so, i am getting 5-8 @ idle.....this seems a little low isn't it....what would i experience if this is the case...My brakes seem fine....

 

If the reading is ACTUALLY 5-8, then your brakes would be hard as a rock after the first application.

Say, you come to a stop at a traffic light. the the light turns green and you pull off ONLY to have to stop immediately for some reason. You'd have virtually no brakes. Pedal would be brick hard.

I recommend you just buy a vaccum gauge from an auto parts store and connect it to a intake manifold source - I use the power brake fitting - and take a reading. Depending on a few variables, like camshaft duration, the reading should be above 12. The shorter the cam duration, the higher the reading should be.

Also, the reading should hold relatively steady, with no sudden dips.

Jake

 

I highly recommend you get a boost/vacuum gauge since your running a blower. Great diagnostic tool.

 

Yes i have one mounted in the pillar pod and noticed it is reading pretty low at idle

 

Try increasing the timing at idle. Maybe somewhere around 32-36*.

 

right now i'm seeing 23-30 degrees at idle using datamaster...would it indicate a vacuum leak if im reading that low? How about if the duration was in the 24x-25x range? what symptoms would i get from a vacuum leak?

 

if your durations are that high probably your only chance for better vacuum is going to be to crank the idle rpms up.

 

Its idling @ 1000, I am very close to cancelling this project.....I am not impressed with it at all..

 

Just try adding the timing. It helped with my cam. What do ya got to loose.

 

its a 93 so i have to get chips burned...its a pain, I sent a datalog to Alvin and when they get settled away in the new shop hes gonna have a lookat it....hopefully he can figure out something...its mostly just numbers to me...lol

 

i dont know crap about 93 model stuff... but isnt there a way to modify your ecm so you can run an emulator of your chip and try changes without burning a new prom?

 

My stroker with a custom cam (22x,23x) and a blower idles at ~900 rpms with 12" vacuum. Your cam is much larger. I'd contact the custom cam designer and ask him what the vacuum should be at idle. My BRE cam is right at where I was told it would be. I also think your idle may be a bit low. Is the car an auto and is the car idle in park or drive?

 

Mine is M6. The idle is set at 875 but it will not idle that low.... I have contacted Bret and just waiting on a reply now.

 

i have a 242/248 and im having vaccum problems on a 12:1 383

 

what problems are you having with low vacuum? any, because you did not post any and you said your brakes are working fine? or are you just upset cause your calculations came up with a low number

stop crunching numbers its a waste, buy a real vacuum gauge their cheap, and figure it out from there